<html>

	<head>
		<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
		<title>点击获取验证码按钮后按钮变灰，倒计时一段时间后又可重复点击</title>
	</head>

	<body>
		<input type="button" id="btn" value="免费获取验证码" onclick="time(this)"/>
		<script type="text/javascript">
			var wait = 3;

			function time(o) {
				if(wait == 0) {
					o.removeAttribute("disabled");
					o.value = "免费获取验证码";
					wait = 3;
				} else {
					o.setAttribute("disabled", true);
					o.value = wait + "秒后可以重新发送";
					wait--;
					setTimeout(function() {
							time(o)
						},
						1000)
				}
			}
		
		</script>
	</body>

</html>